The present invention relates to a hip prosthesis and more particularly to a modular femoral component for a hip prosthesis designed to adapt for an accurate fit in the intramedullary canal, particularly in revision surgery.
The prior art contains many hip prostheses which are constructed to replace the upper portion of the femur. The conventional prosthesis is an unitary structure which is designed to be inserted into the intramedullary canal. To function properly, the prosthetic device must fit snugly into the intramedullary canal. If the fit is loose then the prosthesis will shift positions in relation to the femur causing pain to the patient, interfering with the transmission of power to the leg, and making the hip more vulnerable to re-injury. Because of these problems much of the art attempts to improve the fit of the prosthetic device in the intramedullary canal.
The use of a prosthesis which is constructed of discrete parts is known in the art. Such a prosthesis is shown in European Patent Application No. 257,359 which discloses a discrete stem, body, neck and capitulum. This design is intended to allow the doctor to assemble a prosthesis at the time of implantation.
The use of various inserts in an attempt to obtain a more accurate fit in the intramedullary canal is known in the art. One prosthesis with an insert design is shown in European Patent Application No. 273,871 which discloses a U-shaped insert that wraps around the prosthesis. This design is intended to allow a prosthesis to be used with either the left or right femur depending on the geometry of the U-shaped insert.
Another prosthesis with an insert design is shown in French Patent No. 2,633,509 which discloses the use of inserts on the anterior and posterior surfaces of the prosthesis. The disclosed inserts are intended to more snugly contact the anterior and posterior surfaces of the intramedullary canal.
One problem in the use of prosthetic hip devices is that, following the implantation of the prosthetic device, the intramedullary canal can flair or deform due to osteolysis. The flared or deformed intramedullary canal no longer accurately mates with the prosthetic device and revision surgery is required to replace the originally implanted prosthesis with a more snugly fitting substitute. The solutions proposed in the references discussed above do not adequately address this problem.
There exists, therefore, a need in the art for an improved hip prosthesis which permits a surgeon to modify, during revision surgery, the geometry of the medial portion of the prosthetic device to create a more accurate fit with the deformed or flared intramedullary canal.